Abstract:

The electrocatalytic reduction of nitrate to ammonia (NO₃⁻RR) represents a promising strategy for sustainable nitrogen cycling and the valorisation of wastewater. Its practical implementation, however, is limited by sluggish kinetics, stemming from inefficient proton delivery during the multi-step electron/proton transfer, which restricts both ammonia selectivity and yield. In this work, we report a Pd-Ru bimetallic catalyst supported on nickel foam (Pd-Ru/NF), which functions through a hydrogen shuttle relay mechanism between dual-function sites. Combined experimental and theoretical analyses indicate that Pd sites are principally responsible for nitrate activation and hydrogenation, while adjacent Ru sites efficiently cleave water to supply active hydrogen species (H*). This cooperative interaction creates a dynamic hydrogen-transfer network, enabling rapid and directed proton delivery to reaction intermediates. The relay process not only accelerates the critical hydrogenation steps but also effectively suppresses the competing hydrogen evolution reaction (HER). Consequently, the Pd-Ru/NF electrode attains a notable ammonia yield of 1.77 mmol cm⁻² h⁻¹ with a Faradaic efficiency of 85.95% at −1.4 V vs. RHE. This study establishes a novel catalyst design paradigm based on the management of interfacial hydrogen transfer, providing a general strategy to enhance the efficiency of proton-coupled electrocatalytic transformations.

Key words: Nitrate reduction, Ammonia synthesis, Electrocatalysis, Metal loading